It is known in the prior art that thiols (mercaptans) can be prepared in a process which comprises the addition of hydrogen sulfide to olefins, particularly in the presence of a catalyst, most particularly an acid catalyst. It is further recognized that this process has been applied almost exclusively to the production of tertiary thiols. Markovniokov addition of H.sub.2 S to a "tertiary" olefin, usually an olefin polymer such as a propylene or butylene trimer or tetramer, results in near quantitative selectivity to the tertiary thiol. Exemplification of tertiary thiol preparation from H.sub.2 S and tertiary olefin in the presence of an acidic catalyst is provided by U.S. Pat. Nos. 2,386,769, 2,434,510, 2,464,049, 2,502,596, 2,610,981, 2,950,324, 2,951,875 and 4,102,931.
Certain heterogenous acid catalysts (non-zeolites) including alumina, acid on silica and sulfonic acid exchange resins also convert olefins to thiols. These catalysts are disclosed in U.S. Pat. Nos. 2,951,875, 2,950,324, and 4,582,939 which issued to Goshorn et al., Goshorn et al., and Papay et al. respectively.
X and Y zeolites, and aluminosilicates with FAU structures are used to make tertiary thiols from hydrogen sulfide and an olefin. A method for manufacturing tertiary mercaptans where zeolites are utilized is disclosed in U.S. Pat. No. 4,102,931 that issued to Bucholz.
U.S. Pat. No. 4,638,093 which issued to Fried on Jan. 20, 1987 discloses a process for the preparation of secondary thiols by the addition of H.sub.2 S to C.sub.10 to C.sub.30 linear olefins in the presence of certain zeolite catalysts. The process achieves high selectivity to the secondary thiol and minimizes formation of dialkyl sulfide by-products. The secondary thiol products are of particular advantage for use as intermediates in the preparation of surfactant chemicals.
Nothing disclosed in the prior art teaches the use of MCM-22, HZSM-5, OR HZSM-12 catalysts for making tertiary thiols. Also, there is nothing in the prior art which would suggest that other acidic zeolites will be useful in making tertiary thiols. Examples of acidic zeolites which will not catalyze a reaction of hydrogen sulfide and isobutylene to make t-butylmercaptan include Chabazite, Erionite, ZK-5 and Rho. ZK-5 zeolite is disclosed in U.S. Pat. No. 3,247,195 which issued to Kerr on Apr. 19, 1966.
Therefore, what is needed is a method for making tertiary thiols with MCM-22, HZSM-5, or HZSM-12 catalysts in the presence of hydrogen sulfide and olefins e.g. isobutylene so as to obtain substantially quantitative yields of tertiary thiols.